Filter devices for holding filter elements are readily available commercially in a host of embodiments. A not insignificant portion of production costs in these filter devices is for making the holding means for detachable fixing of the filter element within the housing and for the sealing means for sealing the interior of the filter element relative to the filter housing.
In the filter device described in EP 0891 214 B1, the holding means has a spring configuration of two compression springs which act against one another. By their resulting spring force, an end piece, this is located on the filter element and which acts as a sealing and holding element, is pushed onto a housing-side holding element. The holding element forms a fluid connecting branch formed on the head of the filter housing by a connecting piece which extends into the support pipe of the filter element. The comparatively complex design of the known holding means leads to high production costs. Also, the known solution is less easy to install, in that the filter element can slip unintentionally off the connecting branch or can tilt at this location when put in place. This installation difficulty leads to an adverse effect on the sealing action of the sealing means. In the known solution, the sealing means has an O-ring, preferably of rubber material, which is fixed in the radial internal recess within the end cap of the filter element. In this way, it radially effects sealing relative to the outer peripheral side of the fluid connecting branch of the housing cover or of filter head. This known sealing means with an O-ring is not suited for all fluid media, for example, not for all hydraulic liquids, poorly flammable liquids, corrosive media and for special biodegradable liquids. Depending on the chemical structure of the respective medium, a long-lasting sealing function cannot be ensured.
DE-U-299 22 488 discloses a liquid filter which is easy to install, with a cup-like filter housing, with a removable cover which closes the filter housing, and with an interchangeable filter insert which has its own filter surface. The filter insert is detachably connected to the cover as the filter head of the housing. Furthermore, the known solution has a support mandrel which extends into the filter insert as a connecting branch of a holding means. In the filter housing, connecting and holding means which are referred to as an adapter is provided for the support mandrel, which connecting and holding means are designed as holding elements in the form of retaining fingers. In the known solution, the support mandrel is detachably held in the filter insert. A first installation module has the cover, the filter insert and the support mandrel. A second installation module has the filter housing and adapter with the retaining fingers. During installation of the two installation modules, the adapter is securely connected to the support mandrel. When the filter insert is replaced, the support mandrel remains in the filter housing. In this respect, installation problems (slippage, tilting) can also arise when the filter element has to be pushed onto the support mandrel, for example, when the filter is being replaced on site, with the disadvantageous consequence that the sealing action of the sealing means is adversely affected. The sealing means formed from an O-ring in the radial direction effects support between the support mandrel of the filter housing and the inner peripheral side of the filter element. Although, in addition the support mandrel as a component of the holding means in the longitudinal axial direction parallel to the longitudinal axis of the filter element on its lower base part in a receiving groove has another gasket which is not subject to any further mechanical stress, in any case, as described above the sealing action of the sealing means between the filter element and support mandrel as a housing part is adversely affected.
EP 1 287 871 A1 discloses another filter device with a cup-like filter housing, a filter element therein and holding elements detachably securing the filter element in the filter housing. The holding elements in the known filter device are a receiver located on the filter housing with an undercut forming at least one catch surface. One end of the filter element, projecting, resilient retaining fingers with catch projections form a detachable snap connection by locking to the catch surface of the receiver. In this way, installation and replacement of filter elements can be done by simple locking and releasing of the snap connection. It is sufficient to move the filter element axially in the filter housing in the direction to the cup bottom until the snap connection snaps in place. For dismounting from the cup-shaped housing, the filter element can be simply pulled out. With the known solution, in terms of a means of non-interchangeability, the result is that only filter elements designed especially for the filter device can be used for assuming a function. For example, no other components which are formed optionally as aftermarket elements could endanger the safe use of the filter device.
On the opposite end of the filter element with parts of the holding means, the end cap of the filter element has a fluid connecting branch which can be slipped onto a connecting branch part in the housing cover or filter head. The sealing means is in turn an O-ring which extends radially between the connection parts of the cover part and filter element. In this respect the above described disadvantages also apply to the known filter device according to that European patent.